To my knowledge the most faithful form is "Yaristan" and it implicates a sect in which the fellow disciples are "companions" (~ "yar") to each other as well as to the "mentor" (~ "pír"). The direct meaning of "Yaristan" could be translated "companionship" or "camaraderie". Since the term is chiefly used within Southern Kurdish territories, therefore it is of no surprise to bump against "Yarisan" or "Yarsan" varieties, as you could easily bring these to your mind too: "tawsan" < "tawistan"; "zimsan" < "zimistan", "Kursan" < "Kurdistan".

By the way "Yarésan" or "Yaréstan" are influenced by the Persian pronunciation: "Yaréstan".

I believe so too. I think this is a combined word of Yar - i - Stan. The suffix ~Stan which is so common in Indo-Iranic languages, means "The place" or "Abundant" of the connected word. Your examples make it easy to understand how the Southern dialects short out the /t/ in ~Stan in the combined form. We should realise that exploring the etymology of words in a language such as Kurdish with strong Oral literature rather than recorded written, can not be based on Folk Etymology studies.

It is wise to explore verity of this word in early records of Yaristan, such as 11 centuries.